The proposed research seeks to establish unambiguously the pathway of hydrogen transfer in the interconversion of UDP-galactose catalyzed by UDP-galactose-4-epimerase. The role of enzyme-bound pyridine nucleotide, the role of the enzyme, and the nature(s) of substrate- derived intermediate(s) are to be investigated. It is also proposed to study the mechanistic relationship between electron transfer and group transfer in the reactions catalyzed by pyruvate dehydrogenase complex.